Means for accumulating aircraft position data for a beacon based collision avoidance system and other purposes

Abstract

A protected aircraft having a discrete address beacon transponder includes a ground base air traffic control radar beacon system (ATCRBS) interrogator, a collocated discrete address beacon system (DABS) transponder and a directional antenna on the protected aircraft. The protected aircraft synchronizes a local clock with the pulse repetition frequency (PRF) and scan rate of the ATCRBS interrogating his field of interest from which information the protected aircraft can calculate the azimuth angle of responding intruder aircraft with respect to the ground station. By means of his directional antenna the protected aircraft also determines the azimuth of the intruder with respect to itself. Interrogation by the protected aircraft of a collocated ground DABS transponder or a DME or other suitable means of measuring range provides a data base which together with the aforementioned azimuth angles permits the protected aircraft to calculate instantaneous position of the intruder relative to his own.

The invention claimed is: 
     
       1. Means for use in a beacon based collision avoidance system wherein a fixed station transmits an interrogation message along a relatively narrow beam radiated from the fixed station and wherein said relatively narrow beam is scanned through a field of interest on a discoverable schedule and wherein an aircraft illuminated by said beam normally transponds a first reply message said means for use comprising: an addressable transponder for transmitting a second reply message when addressed, said addressable transponder being arranged in predetermined fixed spatial relationship with said fixed station; and, a protected aircraft comprising:   means for discovering said schedule;   means for transponding a reply message when said protected aircraft is illuminated by said relatively narrow beam;   an interrogator for addressing a message to said addressable transponder whereby said addressable transponder transmits said second reply message, the range between said protected aircraft and said addressable transponder being determined thereby; and,   a directionable antenna means responsive to said range and said schedule for steering a beam therefrom.   
     
     
       2. The means for use in a beacon based collision avoidance system of claim 1 wherein said means for discovering comprises means for receiving interrogations from said fixed station and clock means responsive to the received interrogations from said fixed station to synchronize said clock means with said interrogations.